Organic electroluminescence elements have a simple element structure, and therefore are expected as a light-emitting device for next-generation displays providing a smaller thickness, a lighter weight, a larger area, and lower costs. For this reason, active investigations are now being done in recent years.
Field effect transistors (FET) in an active matrix system using a thin-film transistor (TFT) are understood to be effective as a driving system for driving organic EL devices in terms of operational speed or power consumption. Alternatively, in recent years, active investigations on organic thin film transistors (organic TFT) using organic semiconductor materials are now being done for semiconductor materials that form thin-film transistors, in addition to investigations on inorganic semiconductor materials, such as silicon semiconductors and compound semiconductors, etc. Although such organic semiconductor materials are expected to be a next-generation semiconductor material, they have problems of exhibiting lower charge mobility and higher resistance compared with those of inorganic semiconductor materials.
On the other hand, in field effect transistors, static induction transistors (SIT) in a vertical FET structure have the advantages of shorter channel width of the transistor, higher speed response and more operating power owing to effective use of the whole surface of the electrode, while receiving little effect from the interface thereof, etc.
In recent years, organic light-emitting transistors based on a combination of the SIT structure and an organic EL device structure are now being investigated (see non-patent document 1 and patent documents 1 and 2) utilizing the above-mentioned feature of the static induction transistors (SIT). FIG. 13 illustrates a cross section block diagram of an example of an organic light-emitting transistor based on combination of the SIT structure and the organic EL device structure. This organic light-emitting transistor 101 has a vertical FET structure, as illustrated in FIG. 13, provided with a source electrode 103 having a transparent electric conductive film, a positive hole transporting layer 104 having a gate electrode 105 in a slit shape embedded therein, a light-emitting layer 106, and a drain electrode 107, arranged in this order on a glass substrate 102. The combined organic light-emitting transistor 101 has a structure with a Schottky gate electrode 105 in a slit shape, embedded in the positive hole transporting layer 104, and the positive hole transporting layer 104 and the gate electrode 105 are joined with a Schottky junction, thereby forming a depletion layer in the positive hole transporting layer 104. Since the spread of this depletion layer varies with the gate voltage, the channel width is controlled by variation of the gate voltage (voltage applied between the source electrode 103 and the gate electrode 105), and thereby the generated amount of charge is varied by control of the applied voltage between the source electrode 103 and the drain electrode 107.
In addition, FIG. 14 is a cross section block diagram illustrating an example of an organic light-emitting transistor based on combination of a bottom contact type FET structure and an organic EL device structure described in patent document 2. This organic light-emitting transistor 111 has a structure, wherein an auxiliary electrode 113 and an insulating layer 118 are laminated on a substrate 112, an anode 115 is formed on the insulating layer 118, a light-emitting material layer 116 is formed so as to cover the anode 115 on the insulating layer, and furthermore a cathode 117 is formed thereon, as illustrated in FIG. 14. An anode buffer layer 119 is formed on the anode 115 for passing a positive hole from the anode 115 to the light-emitting material layer 116 and simultaneously for preventing an electron passing from the light-emitting material layer 116 to the anode 115. Also in this organic light-emitting transistor 111, the channel width is controlled by variation of the applied voltage between the auxiliary electrode 113 and the anode 115, and the generated amount of the charge is varied by control of the applied voltage between the anode 115 and the cathode 117.                [Non-patent document 1]: Kazuhiro Kudo “The present circumstances and future view of organic transistors”, Oyo Butsuri, the 72nd volume, No. 9, pages 1151 to 1156 (2003)        [Patent document 1]: Japanese laid-open application No. 2003-324203 (Claim 1)        [Patent document 2]: Japanese laid-open application No. 2002-343578 (FIG. 23)        